modern humans

Two reports came out last week in the journal Nature, re-dating some European human fossils to before 40 thousand years ago (kya), a few thousand years older than previous evidence for modern-looking people in the region. The media have been reporting these studies as revealing “the first Europeans,” but of course we all know that the first Europeans were the badass hominids, my favorites, from the 1.8 million year old site of Dmanisi.

KC4 maxilla (Higham et al. 2011)

From Kent’s Cavern (United Kingdom) is a partial maxilla, now dated to 44 – 41 kya* (Higham et al. 2011; but see below). The jaw fragment with highly worn teeth was found just above some Aurignacian-like (Upper Paleolithic) blades in 1927. [NB below these 2 blades were 2 other blades of a tool “complex…tentatively associated with Neandertals] The laughable amount of bone makes it rather impossible to say whether the fossil represents a Neandertal or more modern-looking human. The authors examined what little of the morphology was left and concluded that the fossil shared the most similarities with recent humans but only a few with Neandertals. A more rigorous analysis of what this mix of traits means would have been nice (i.e. why would an individual have derived traits of both ‘modern’ humans and Neandertals?). The researchers tried to extract DNA for analysis, but apparently organic remains were too poorly preserved for a good analysis. Bummer.

Cavallo B and C (Benazzi et al. 2011)

A similar older-than-we-thought story is reported by Stefano Benazzi and buddies, who reanalyzed teeth from the Italian site of Grotta del Cavallo (left). After the site was excavated in 1967, the teeth were attributed to Neandertals and the lithics classified as “Uluzzian.” I would be a dirty liar if I said knew anything about the “Uluzzian” industry (try this other site which may be more informative), but apparently it’s seen as transitional between the Neandertal-associated Mousterian and ‘more advanced’ Upper Paleolithic toolkits. So this assemblage could be used to argue that Neandertals were smart enough to upgrade to a sexier stone tool industry shortly before their anatomy (but not their genes!) disappeared. BUT! also like in Kent’s Cavern paper, Benazzi and colleagues examined what little morphology is preserved in the fossil teeth, and (re)assigned them to modern-looking humans. The authors provided nice qualitative and quantitative arguments for the human status of the teeth, though again I have to raise caution that these are only teeth and we have no idea what the rest of the skeleton would have looked like. Researchers also analyzed shells associated with the now-human teeth and dated the site to around 44 kya, making them the oldest probably-human remains in Europe.

Now, according to conventional wisdom, the Neandertals were dullards who made and used the Mousterian stone tool industry. The Mousterian was nice and all, but not nearly as wicked-pisser as the smart and sassy modern-looking humans’ Aurignacian toolkit. The thing is, though, there really hasn’t been really a lot of evidence unequivocally linking modern-looking fossils with Aurignacian artifacts. So both of the recent studies in Nature lend support to the idea that maybe modern humans were the sole makers (and users) of an advanced stone tool industry. But it’s important to remember [1] that the blades ‘associated’ with the Kent’s Cavern jaw can’t really be definitively attributed to a stone tool industry; [2] the blades were deeper in the cave than the jaw, and so may actually be appreciably older than the jaw; and [3] while the teeth from Kent’s Cavern and Cavallo do look most comparable to those belonging to ‘anatomically’ modern humans, we don’t know what the skulls or skeletons containing the teeth looked like. All that said, it’s neat to see the possible appearance of certain anatomy and technology in Europe thousands of years earlier than previously thought. It also re-raises the issue of the degree to which modern-looking humans and Neandertals overlapped in space and time, and what these interactions would have been like (I’d guess terrifying, hilarious and/or sexy).

KC4 originally(Higham et al. 2011)

A fun lesson also comes from the Kent’s Cavern study. Higham and colleagues report that the KC4 human maxilla was excavated in 1927 and analyzed by Sir Arthur Keith, a well-trained anatomist and paleoanthropologist famous in his day. Keith described the fossil as containing a canine, second premolar and first molar (right, compare with above). Higham and colleagues, however, noticed that what Keith described as a second premolar was in fact a first premolar. The teeth are so worn they mostly lack information about their form and features, so this mistake probably didn’t really mislead anatomists in any way. Still, it goes to show that even experts like Keith can make mistakes or overlook the things they know best, and this is not the first time I’ve seen this happen with fossils. So always (politely) question those giants whose shoulders you’re standing upon.

*Update (07 Nov): John Hawks points out that the KC4 maxilla itself was not used to obtain the older radiocarbon age estimate. In 1989 the maxilla was directly dated to around 30 kya, over 10 ky younger than the new estimates. Higham and friends thought this date was too young, based on methodological grounds. An attempt to redate the KC4 maxilla based on one of the teeth yielded too little collagen (organic material) to produce a date. Bummer again! The new estimate is instead based on radiocarbon dates obtained from animal bones that were excavated from above and below the human jaw. So this ‘redating’ of the Kent’s Cavern maxilla is very interesting, but should be taken with a grain of salt.

“These results suggest admixture between Denisovans or a Denisova-related population and the ancestors of East Asians, and that the history of anatomically modern and archaic humans might be more complex than previously proposed.“

I’m sure it will turn out to be more complex still. Onward and upward!

2010 was a big year for anthropology and lawn-chair-anthropologists. There was laughter and crying, and maybe also some yelling. And smiling. Let’s take a look back at some of the big events of the past year.

Ancient DNA. What a great year for ancient human DNA! In April, Krause and colleagues (2010) announced the sequencing of mitochondrial DNA from a ~50,000 year old girl from Denisova in Siberia. This sequence was twice as divergent from humans as Neandertal mtDNA, which really shocked a lot of people. Then just a week or so ago Reich and colleagues (2010) announced nuclear DNA from the site. The big news was that these ancient humans contributed genes to modern day Melanesians, but not other modern humans sampled. In May, Green and the Pääbo lab announced a draft sequence of the Neandertal nuclear genome. Like with the Denisova story, Neandertal mtDNA is fairly distinct from that of modern humans, and the nuclear genome revealed contribution to some modern humans but not to others. Basically, ancient DNA came out supporting the multiregional model of modern human origins.

Malapa hominids. Lee Berger and researchers announced a new fossil site, Malapa, in South Africa. This site yielded 2 partial skeletons (and others forthcoming), including a very well-preserved skull of a subadult. Superficially the thing looked to me like Australopithecus africanus, though the authors argue that it shows some features derived toward the condition of early Homo. But at an estimated 1.9-1.7 million years old, it’s a little too young to have anything to do with the origin of Homo – not to mention its small 400 cubic centimeter cranial capacity. I really don’t know what to do with Malapa yet.

Woranso-Mille Australopithecus afarensis. This site dates to around 3.6 million years ago, so it’s roughly contemporaneous with Laetoli afarensis, or intermediate in age between Laetoli and later afarensis sites like Maka and Hadar. Haile-Selassie and colleagues described a partial skeleton from the site. This male includes part of the pelvis, which didn’t get much coverage. But it has a 1st rib, scapula and clavicle, indicating a fairly human-like (rather than ape-like) torso shape. So even for how well we know A. afarensis, we’re always learning more about our ancestor.

Saadanius hijazensis and catarrhines. I didn’t blog about this one at the time as I was getting ready to hit the field. But this was exciting because Iyad Zalmout and friends here at UM discovered and analyzed it. Saadanius was found in ~29 million year old deposits in Saudi Arabia, right around the estimated time of origins of apes. The fossil looks like an Aegyptopithecus to my untrained eye, but apparently may be similar to the last common ancestor of apes and old world monkeys.

Field work. I had my first (of hopefully more!) field season at Dmanisi in Georgia. Paleoanthropology would be nothing without fossils, so an important aspect of the job I’d like to do more of is increasing the fossil record. Dmanisi is an amazing place for this, being among the oldest human sites outside Africa, and the interesting ‘intermediacy’ of the Dmanisi hominids between early Homo and more classic H. erectus. We found some great stuff last year, and I anticipate the site will produce more great fossils in the future. Who knows, maybe more fossiliferous deposits will be found in nearby regions?

So it was a helluva year, 2010. What excitement will 2011 bring? Here are some things I’d like to, or expect to, see this year:

More ancient DNA – the surprise that many researchers got from Denisova and Neandertal ancient DNA clearly warrants more work on other ancient DNA. What does that of other fossil humans look like? Will the picture of human origins become further complicated (that is, different from paradigmatic out-of-Africa replacement)? In this regard we need to analyze DNA from more late Pleistocene fossils regarded as ‘anatomically modern.’

a) More about Malapa. I want to say I heard somewhere that there were more hominids than just the 2 presented in the Science paper. These additional specimens will provide further evidence, including what variation within the site was like, and how it fits with other South African specimens. From the appearance of things, these fossils may be late-persisting A. africanus, somehow contemporaneous (roughly sympatric?) with A. robustus and possibly early Homo. Perhaps more work on the geology and taphonomy of Malapa will show it to be older, contemporaneous with the nearby site of Sterkfontein known for abundant A. africanus fossils? Probably not.

b) More hominid sites and fossils in South Africa. One thing that was neat about Malapa was that it was from slightly outside the rest of the South African ‘cradle’ sites like Sterkfontein, Kromdraai, Drimolen, and Swartkrans. When I was in the area in 2008 I went with some researchers on survey of the Sterkfontein valley, new sites are definitely being sought. Perhaps 2011 will see the discovery of more Malapa-like sites?

Human fossils from East Asia. Maybe even ancient DNA recovery from the region. East Asia has long been thought to be a potential ‘center’ of human origins. Earlier in the year, fossils coming from Zhirendong suggest some of the earliest evidence of chin, arguably a ‘modern human’ feature. Recent fossil and genetic discoveries ought to usher a renewed vigor in examining human evolution in Asia.

Perusing my AJPA RSS feed, I came across an interesting abstract (see attempt at citation below). This article tests three different hypotheses for cranial robusticity in modern humans: genetic, mastication, and climate, and finds that mastication doesn’t seem to explain the robusticity of some populations. I didn’t read the article, just the abstract (it’s summer, and I was perusing), but it got me thinking. If we find population variation that is not based on climate or diet within modern humans, could this have been the case in more ancient hominids? My memory for australopithecine crania is terrible, but I keep thinking of all the different sized “erectines” and “habilines” we looked at in 565 – that sample definitely represented different levels of robusticity. I’m not really sure where I’m going with this (I probably should have read the article and thought about it for a day or so to collect my thoughts, but I’m impatient and felt like posting). I guess I’m just trying to link what we know about modern humans to what we think we know about other hominids. Thoughts? Did anyone else look at this article? Did you find it interesting or dull or poorly written or irrelevant? Is everyone having a good summer so far?

Yesterday, two articles of interest to anthropologists were published in the the journal Nature‘s advance online publication. First is the announcement of a very complete bone flute, and fragments of other flutes, dating to around 35,000 thousand years ago from Germany. The finds come from the site of Hohle Fels in Southern Germany; a few months ago it was announced that the site produced the earliest Venus figurine. Venus figurines are some of the earliest pieces of carved art produced by humans, and are figures of corpulent women with corpulent lady-parts. This latter fact captures the popular imagination as the earliest ‘porn,’ but in truth no one’s sure what exactly they mean, although many researchers think they’re related to fertility. Anyway, the flutes are found in Aurignacian deposits, which by and large are attributed to ‘anatomically modern’ humans, as opposed to the contemporaneous Neandertals. The final sentences of the paper sum things up nicely:

“…early Upper Paleolithic music could have contributed to the maitenance of larger social networks, and thereby may have helped facilitate the demographic and territorial expansion of modern humans relative to culturally more conservative and demographically more isolated Neanderthal populations.”

I like their use of “culturally more conservative” description of Neandertals, whereas in the past the phrasing probably would have been “culturally primitive” or “…less advanced.” “Conservative” is certainly an interesting way to describe cultural differences between Neandertals and other Upper Paleolithic populations. I wonder if Neandertals were also more God-fearing and homophobic, as I understand ‘conservative’ to mean nowadays…

The second topic will have to wait. I just got invited to have dinner and drinks and watch soccer, which I’d be silly to pass up. Go South Africa!

[Hey, I’ll bet I’m the first person to make that allusion…]In a paper published in JHE today, M. Schillaci posits that human facial anatomy suggests the existence of two human lineages in the late Pleistocene. Schillaci’s analysis reveals that faces of early Australasian crania (40-8 ka) are very similar to those of Levantine specimens Skhul 5, Qafzeh 6 and Qafzeh (100-90 ka). The overall results of the study suggest that the Australasian and Levantine populations share an earlier common ancestor than modern humans, including Upper Paleolithic Europeans. Schillaci interprets this to mean that modern humans first dispersed from Africa around 100 ka, long before the supposed “revolution” of Paleolithic Europe, and made it as far as Australia; second dispersal then occurred some 50 ka later.

The article brings up the issue of Out-of-Africa (Replacement) vs. Multiregional models, but does not clearly come out directly in favor of either one. But by setting up a scenario in which two human lineages are present throughout the Old World in the last 100 ka, the possibility is opened up for these lineages to accrue genetic differences simply by drift or even by selection, then to come into contact again and admix, and for the “archaic” genes to be incorporated into the newer (and modern) genome (introgressive hybridization; cf Evans et al. 2006, Garrigan and Kingan 2007, Hawks and Cochran 2006).

Schillaci does note that the Levantine sample

exhibits a slightly closer genetic relationship to Neandertals (d=0.7318) than to Upper Paleolithic Europeans (d=0.7483). . . . This observed relationship is probably not the result of phenotypic convergence, and likely reflects a slightly more recent common ancestry and/or perhaps hybridization between early modern humans and Neandertals (Trinkaus, 2007). (p. 6)

However, he later notes,

In the present study, the relationship between early modern humans from the Levant and early Australasians (d=0.348) is more than 2.1 times closer than between early modern humans and Neandertals (d=0.7318), and Neandertals do not show a close relationship with early Australasians (d=1.2615). If the observed relationship between Neandertals and early modern humans is the product of hybridization, there is no craniometric evidence indicating that there was substantial introgression of Neandertal alleles into the dispersing modern human population… (p. 7)

Can Schillaci make these claims about “genetic relationship[s]” based on his data? Let’s look at the opening line of the abstract: “This study examines the genetic affinities of various modern human groupings using a multivariate analysis of morphometric data.” A rewording might be: This study examines the craniofacial affinities of various modern human groupings, and to thereby infer genetic relationships. Basically, Schillaci assumes that genetic relationships between populations are accurately reflected in facial anatomy, a bold statement to make. Indeed, he acknowledges the problems with this assumption, but also cites studies (which I haven’t yet read) suggest that craniometric variation in humans throughout the world fits a neutral model of genetic variation. So, Schillaci talks about genetic relationships throughout the paper, but these aren’t based on actual genetic data, but rather inferences from craniometric data–quite confusing. His aforementioned lack of evidence for introgression between neandertals and early modern humans does not preclude real genetic evidence for introgression (cf. what I cf-ed above.)

What I care about: the study allows for, and possibly corroborates, a Multiregional model of human evolution (of course, what I really care about is the possibility of such a model prior to, and in the early stages of, the genus Homo). Hey, I guess old-school craniometrics hasn’t outlived its usefulness in physical anthropology.

Last year, John Hawks and team wrote about how evolution has been accelerated in recent human evolution, esp. in the past 40 kya or so. A day or two ago Barreiro ed amici wrote about recent natural selection in modern humans. When it comes to genetics (and to science, as long as we’re being candid) I’m fairly green, so if you want to read a good news brief about this interesting paper, check out Ann Gibbons’s coverage in Science. Basically, the selection-seeking squad analyzed 2.8 million single nucleotide polymorphisms (SNPs) from 210 people from Africa, Asia and Europe. They identified hundreds of genes that appear to have been the targets of fairly recent selection. In some areas of the genome, esp. those related to diseases, negative selection appears to have reduced differentiation between the three continents. Conversely, positive selection has increased diversity, presumably as populations have adapted to local environments.

The authors point out that their methods pave the way for important research to be done on diseases with genetic predispositions, esp. those correlated with ethnicity. It’s pretty cool stuff, but another thing I found really interesting was this paragraph:

Of note, among the highly differentiated genes with known functions, several control variable morphological traits in humans (Table 1). Furthermore, most of these genes are pleiotropic: that is, they are individually involved in several different traits. for example, EDAR regulates hair follicle density and the development of sweat glands and teeth in humans and mice [24, 25]. In humans, selective pressures on EDAR favoring changes in body temperature regulation and hair follicle density in response to colder climates may have influenced tooth shape, although this trait probably does not affect population fitness. This anecdotal example shows how ‘phenotypic hitchhiking’ in genes under positive selection may have substantially increased the observed number of physiological and morphological traits differentiating modern human populations. (p. 4)

One of the shortcomings of paleoanthropology is poor understanding of the genetic basis for various aspects of skeletal morphology, which is just about all the benevolent fossil record gives us; that is to say, it can be difficult to determine whether characters (i.e. “brow ridges”) are determined by genes, environment, complex interaction between genes and environment, complex interaction between different genes (epistasis), etc. Because of the pleiotropic effects of EDAR, discerning which aspects of the phenotype were shaped by selection becomes difficult. In the course of human evolution, did the loss of body hair (compare most humans to any primate) coincide with dental evolution, and if so, how does this affect our understanding of selective forces shaping hominin evolution? Or, can hominin dental evolution tell us anything about the evolution of body hair or sweat glands? These are interesting questions that could really only be asked as the functional properties of the genome begin to be uncovered. Of course, they can probably only be best answered when we know more about the true functions and frivolities of genes.